<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
</head>
<link rel="stylesheet" href="../common.css" />
<style>
    canvas {
        position: absolute;
        width: 100%;
        height: 100%;
    }
</style>

<body>
    <canvas id="canvasBox"></canvas>
</body>
<script>
    var settings = {
        particles: {
            length: 500, // maximum amount of particles
            duration: 2, // particle duration in sec
            velocity: 100, // particle velocity in pixels/sec
            effect: -0.75, // play with this for a nice effect
            size: 30, // particle size in pixels
        },
    };
    (function () {
        var b = 0;
        var c = ["ms", "moz", "webkit", "o"];
        for (var a = 0; a < c.length && !window.requestAnimationFrame; ++a) {
            window.requestAnimationFrame = window[c[a] + "RequestAnimationFrame"];
            window.cancelAnimationFrame =
                window[c[a] + "CancelAnimationFrame"] ||
                window[c[a] + "CancelRequestAnimationFrame"];
        }
        if (!window.requestAnimationFrame) {
            window.requestAnimationFrame = function (h, e) {
                var d = new Date().getTime();
                var f = Math.max(0, 16 - (d - b));
                var g = window.setTimeout(function () {
                    h(d + f);
                }, f);
                b = d + f;
                return g;
            };
        }
        if (!window.cancelAnimationFrame) {
            window.cancelAnimationFrame = function (d) {
                clearTimeout(d);
            };
        }
    })();

    /*
     * Point class
     */
    var Point = (function () {
        function Point(x, y) {
            this.x = typeof x !== "undefined" ? x : 0;
            this.y = typeof y !== "undefined" ? y : 0;
        }
        Point.prototype.clone = function () {
            return new Point(this.x, this.y);
        };
        Point.prototype.length = function (length) {
            if (typeof length == "undefined")
                return Math.sqrt(this.x * this.x + this.y * this.y);
            this.normalize();
            this.x *= length;
            this.y *= length;
            return this;
        };
        Point.prototype.normalize = function () {
            var length = this.length();
            this.x /= length;
            this.y /= length;
            return this;
        };
        return Point;
    })();

    /*
     * Particle class
     */
    var Particle = (function () {
        function Particle() {
            this.position = new Point();
            this.velocity = new Point();
            this.acceleration = new Point();
            this.age = 0;
        }
        Particle.prototype.initialize = function (x, y, dx, dy) {
            this.position.x = x;
            this.position.y = y;
            this.velocity.x = dx;
            this.velocity.y = dy;
            this.acceleration.x = dx * settings.particles.effect;
            this.acceleration.y = dy * settings.particles.effect;
            this.age = 0;
        };
        Particle.prototype.update = function (deltaTime) {
            this.position.x += this.velocity.x * deltaTime;
            this.position.y += this.velocity.y * deltaTime;
            this.velocity.x += this.acceleration.x * deltaTime;
            this.velocity.y += this.acceleration.y * deltaTime;
            this.age += deltaTime;
        };
        Particle.prototype.draw = function (context, image) {
            function ease(t) {
                return --t * t * t + 1;
            }
            var size = image.width * ease(this.age / settings.particles.duration);
            context.globalAlpha = 1 - this.age / settings.particles.duration;
            context.drawImage(
                image,
                this.position.x - size / 2,
                this.position.y - size / 2,
                size,
                size
            );
        };
        return Particle;
    })();

    /*
     * ParticlePool class
     */
    var ParticlePool = (function () {
        var particles,
            firstActive = 0,
            firstFree = 0,
            duration = settings.particles.duration;

        function ParticlePool(length) {
            // create and populate particle pool
            particles = new Array(length);
            for (var i = 0; i < particles.length; i++)
                particles[i] = new Particle();
        }
        ParticlePool.prototype.add = function (x, y, dx, dy) {
            particles[firstFree].initialize(x, y, dx, dy);

            // handle circular queue
            firstFree++;
            if (firstFree == particles.length) firstFree = 0;
            if (firstActive == firstFree) firstActive++;
            if (firstActive == particles.length) firstActive = 0;
        };
        ParticlePool.prototype.update = function (deltaTime) {
            var i;

            // update active particles
            if (firstActive < firstFree) {
                for (i = firstActive; i < firstFree; i++)
                    particles[i].update(deltaTime);
            }
            if (firstFree < firstActive) {
                for (i = firstActive; i < particles.length; i++)
                    particles[i].update(deltaTime);
                for (i = 0; i < firstFree; i++) particles[i].update(deltaTime);
            }

            // remove inactive particles
            while (
                particles[firstActive].age >= duration &&
                firstActive != firstFree
            ) {
                firstActive++;
                if (firstActive == particles.length) firstActive = 0;
            }
        };
        ParticlePool.prototype.draw = function (context, image) {
            // draw active particles
            if (firstActive < firstFree) {
                for (i = firstActive; i < firstFree; i++)
                    particles[i].draw(context, image);
            }
            if (firstFree < firstActive) {
                for (i = firstActive; i < particles.length; i++)
                    particles[i].draw(context, image);
                for (i = 0; i < firstFree; i++) particles[i].draw(context, image);
            }
        };
        return ParticlePool;
    })();

    /*
     * Putting it all together
     */
    (function (canvas) {
        var context = canvas.getContext("2d"),
            particles = new ParticlePool(settings.particles.length),
            particleRate = settings.particles.length / settings.particles.duration, // particles/sec
            time;

        // get point on heart with -PI <= t <= PI
        function pointOnHeart(t) {
            return new Point(
                160 * Math.pow(Math.sin(t), 3),
                130 * Math.cos(t) -
                50 * Math.cos(2 * t) -
                20 * Math.cos(3 * t) -
                10 * Math.cos(4 * t) +
                25
            );
        }

        // creating the particle image using a dummy canvas
        var image = (function () {
            var canvas = document.createElement("canvas"),
                context = canvas.getContext("2d");
            canvas.width = settings.particles.size;
            canvas.height = settings.particles.size;
            // helper function to create the path
            function to(t) {
                var point = pointOnHeart(t);
                point.x =
                    settings.particles.size / 2 +
                    (point.x * settings.particles.size) / 350;
                point.y =
                    settings.particles.size / 2 -
                    (point.y * settings.particles.size) / 350;
                return point;
            }
            // create the path
            context.beginPath();
            var t = -Math.PI;
            var point = to(t);
            context.moveTo(point.x, point.y);
            while (t < Math.PI) {
                t += 0.01; // baby steps!
                point = to(t);
                context.lineTo(point.x, point.y);
            }
            context.closePath();
            // create the fill
            context.fillStyle = "#ea80b0";
            context.fill();
            // create the image
            var image = new Image();
            image.src = canvas.toDataURL();
            return image;
        })();

        // render that thing!
        function render() {
            // next animation frame
            requestAnimationFrame(render);

            // update time
            var newTime = new Date().getTime() / 1000,
                deltaTime = newTime - (time || newTime);
            time = newTime;

            // clear canvas
            context.clearRect(0, 0, canvas.width, canvas.height);

            // create new particles
            var amount = particleRate * deltaTime;
            for (var i = 0; i < amount; i++) {
                var pos = pointOnHeart(Math.PI - 2 * Math.PI * Math.random());
                var dir = pos.clone().length(settings.particles.velocity);
                particles.add(
                    canvas.width / 2 + pos.x,
                    canvas.height / 2 - pos.y,
                    dir.x,
                    -dir.y
                );
            }

            // update and draw particles
            particles.update(deltaTime);
            particles.draw(context, image);
        }

        // handle (re-)sizing of the canvas
        function onResize() {
            canvas.width = canvas.clientWidth;
            canvas.height = canvas.clientHeight;
        }
        window.onresize = onResize;

        // delay rendering bootstrap
        setTimeout(function () {
            onResize();
            render();
        }, 10);
    })(document.getElementById("canvasBox"));
</script>

</html>